For the vast majority of South Central Nebraska, this Friday simply featured varying amounts of much-needed rain from scattered-to-widespread showers and weak thunderstorms streaming across the area from south-southeast to north-northwest. However, one particular storm had other ideas during the mid-late afternoon, as it intensified and ended up spawning a few weaker tornadoes and localized, severe straight-line winds while tracking through the hearts of Hamilton and Merrick counties, causing some damage in rural areas but fortunately no human injuries. Although the finer details of the exact tornado touchdowns/locations proved a bit murky given that ground circulations were primarily intermittent/weak along with a lack of reported damage (Hamilton County) and a lack of concrete photographic evidence of a tornado (Merrick County) officially three tornadoes were declared (chronological order): 1) an EF-unknown with a nearly five-mile, south-to-north path from a few miles west of the Interstate 80 Aurora exit to just northwest of Aurora itself (no known damage)...2) a brief EF-unknown with a roughly one-mile, south-to-north track through fields near Highway 14 east of Marquette (no known damage)...3) an EF-0 with a four-mile, southeast-to-northwest path through rural areas four to eight miles northwest of Central City. This Merrick County EF-0 was the only one that produced confirmed damage, although some of it was likely also associated with an accompanying/nearby swath of straight line winds estimated up to around 80 MPH. Most notably, a large cattle feedlot four miles north-northwest of Central City sustained a variety of damage, including a portion of a large confinement building destroyed along with some outdoor pens and livestock shade structures. In addition, four head of cattle were reportedly injured, including two that had to be euthanized. Although this was the only known occurrence of concentrated structural damage, several irrigation pivots and a few trees were toppled, and an unoccupied tractor windshield was blown out. Turning to the Hamilton County tornado paths, there were no confirmed damage reports and the Emergency Manager characterized them as mainly broad/weak ground circulations (visually more resembling landspouts). That being said, the community of Aurora narrowly avoided a direct hit, as a KLKN-TV web cam captured a dusty circulation passing over Highway 34 on the extreme west side of town.
Digging into the timing and meteorological background behind this rogue severe/tornadic storm, and starting from a forecast perspective, especially the tornadic aspect was largely an unanticipated surprise. All convection prior to this storm's development had been quite weak, and instability/shear parameters offered little hint of severe weather in the immediate area. The 20 UTC (3 p.m. CDT) Day 1 Convective Outlook from SPC called for only general thunder in the Hamilton/Merrick area, with the eastern fringes of a categorical Marginal Risk category (level 1 of 5) residing a good 100 miles off to the west. In the mid-upper levels, a large-scale (but weak/unprogressive) upper trough was positioned along a northwest-southeast axis over the western United States, while an upper ridge was centered over the Upper Great Lakes, and the net influence of these features placing South Central Nebraska under modest south-southeasterly flow aloft. At the surface, there was also an absence of noteworthy features, with fairly light south-southeast breezes supporting a seasonably-moist airmass with dewpoints into the low-60s (F). On the finer mesoscale level, there was likely at least a subtle boundary in the area prior to storm development...perhaps an outflow boundary kicked out from earlier/ongoing showers and weak storms, and perhaps also augmented by a differential-heating boundary (the latter evidenced by a modest surface temperature difference at 4 p.m. CDT between a rain-cooled 68 degrees at Hastings versus 81 at Aurora). No matter what ultimately caused this mesoscale accident to unfold, the storm made its presence known during its 1 hour, 45-minute lifespan, first gaining strength over the Clay/Hamilton County line around 3:45 p.m. CDT, crossing into Merrick County around 4:30 p.m. CDT, and rapidly weakening around 5:30 p.m. CDT while entering southwestern Nance County.